GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2000 🢒 Sonoma Pickup - 2WD 🢒 DTC 🢒 DTC P0446 Evaporative Emission (EVAP) Vent System Performance

Object Number: 387281 Size: LF
Engine Controls Components
Fuel Level and Fuel Tank Pressure Sensors
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

System Description

The EVAP System includes the following components:

    • The fuel tank
    • The EVAP vent valve
    • The fuel pipes and hoses
    • The fuel fill cap
    • The EVAP vapor pipes
    • The EVAP purge pipes
    • The EVAP canister
    • The EVAP canister purge valve

A RESTRICTED or BLOCKED EVAP VENT PATH is detected by monitoring fuel tank pressure during normal operation (EVAP vent valve open, EVAP canister purge valve normal). With the EVAP vent valve open, vacuum level in the system should be very low unless the vent path is blocked.

Conditions for Running the DTC

All conditions for P0440 and P0442 have been met and Passed.

Conditions for Setting the DTC
    •  Fuel tank pressure is less than -10 inches H2O.
    •  The condition is present for up to 30 seconds.

Action Taken When the DTC Sets
    • The PCM will illuminate the MIL during the second consecutive trip in which the diagnostic test has been run and failed.
    • The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.

Conditions For Clearing the MIL/DTC
    • The PCM will turn the MIL OFF during the first trip in which the diagnostic has been run and Passed.
    • The history DTC will clear when the PCM turns OFF the MIL.
    • The DTC can be cleared by using the scan tool.

Diagnostic Aids

The following conditions will set DTC P0446.

    •  Faulty EVAP vent valve (stuck closed).
    •  Plugged, kinked or pinched vent hose.
    •  Shorted EVAP vent valve driver circuit.
    •  Plugged EVAP canister.

If the DTC is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set.

If the condition is intermittent refer to Intermittent Conditions .

Test Description

The numbers below refer to the step numbers on the Diagnostic Table.

  1. This step verifies that a fuel tank pressure sensor circuit is not causing the condition.

    2.

  2. This step verifies that the Fuel Tank Pressure sensor responds to a change in vacuum.

    3.

  3. This step isolates the EVAP system from the Fuel Tank Pressure sensor. A Fuel Tank Pressure sensor that does not correctly respond to pressure (or vacuum) causes this DTC to set.

    The Fuel Tank Pressure sensor range is from 7.5 in. H2O of pressure to -17.5 in. H2O of pressure (vacuum).

    4.

  4. This step tests the EVAP vent valve circuits. If the EVAP vent valve clicks when commanded ON and OFF, then the PCM and wiring are OK.

Step

Action

Values

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2
  1. Turn OFF the ignition.
  2. Remove the fuel tank cap.
  3. Turn ON the ignition with the engine OFF.
  4. Monitor the fuel tank pressure sensor voltage with a scan tool.

Is the fuel tank pressure sensor voltage less than the specified value?

4V

Go to Step 3

Go to DTC P0453 Fuel Tank Pressure Sensor Circuit High Voltage

3
  1. Start the engine.
  2. Command the EVAP purge valve ON with a scan tool.
  3. Raise the engine speed to 1200 RPM.
  4. Monitor the fuel tank pressure sensor voltage with a scan tool for 1 minute.

Does the fuel tank pressure sensor voltage increase to more than the specified value?

4.5V

Go to Step 6

Go to Step 4

4

Does the fuel tank pressure voltage change when the EVAP canister purge valve is enabled?

--

Go to Diagnostic Aids

Go to Step 5

5

  1. Turn OFF the ignition.
  2. Remove the fuel tank pressure sensor. Refer to Fuel Tank Pressure Sensor Replacement .
  3. Turn ON the ignition with the engine OFF.
  4. Connect the hand held vacuum pump J 23738-A to the vacuum port of the fuel tank pressure sensor.
  5. Attempt to apply a vacuum up to the specified value with the hand vacuum pump.
  6. Monitor the fuel tank pressure with a scan tool.

Does the fuel tank pressure change as vacuum is applied?

10 in Hg

Go to Step 6

Go to Step 16

6
  1. Turn OFF the ignition.
  2. Inspect the EVAP system for the following conditions:
    3. • Improperly routed, kinked or damaged EVAP purge and tank vent lines.
    • A damaged EVAP system component.
  3. Repair the EVAP system as necessary if you find a condition.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 7

7

Command the EVAP vent valve ON and OFF with a scan tool. Refer to

EVAP Canister and EVAP Vent Valve (4DR Utility and Pickup)


Object Number: 235181 Size: LF
(1)Evaporative (EVAP) Vent Solenoid Valve
(2)Crossmember
(3)EVAP Canister
(4)Fuel Tank
(5)Fuel Tank Sender Assembly
.

Do you hear an audible click as the EVAP vent valve is commanded ON and OFF.

--

Go to Step 8

Go to Step 10

8
  1. Turn OFF the ignition.
  2. Disconnect the fuel tank vapor line and the EVAP purge line from the EVAP canister.
  3. Plug the EVAP canister port for the fuel tank vapor line with an appropriate plug.
  4. Connect the hand held vacuum pump J 23738-A to the EVAP purge line canister fitting.
  5. Turn ON the ignition with the engine OFF.
  6. Command the EVAP vent valve ON (closed) with a scan tool.
  7. Attempt to apply and hold the specified amount of vacuum with the hand held vacuum pump.
  8. Command the EVAP vent valve OFF (open) while monitoring the hand held vacuum pump gauge.

Does the vacuum drop from the specified value when the EVAP Vent Valve is opened?

5 in. Hg.

Go to Step 13

Go to Step 9

9

Remove the plug from the vent line while monitoring the hand held vacuum pump gauge.

Does the vacuum drop from the specified value when the vent line is unplugged?

5 in. Hg.

Go to Step 14

Go to Step 12

10
  1. Disconnect the EVAP vent valve harness connector.
  2. Probe the control circuit of the EVAP vent valve with a test lamp connected to B+.

Is the test lamp illuminated?

--

Go to Step 11

Go to Step 14

11

Test the control circuit of the EVAP vent valve for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 17

12
  1. Inspect the EVAP vent line from the EVAP canister to the EVAP vent valve for restrictions.
  2. If you find a condition repair as necessary.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 15

13

Repair the restriction between the fuel tank pressure sensor and the EVAP canister.

Did you complete the repair?

--

Go to Step 18

--

14

Replace the EVAP Vent Valve. Refer to Evaporative Emission Vent Valve Replacement .

Did you complete the replacement?

--

Go to Step 18

--

15

Replace the EVAP Canister. Refer to Evaporative Emission Canister Replacement .

Did you complete the replacement?

--

Go to Step 18

--

16

Replace the Fuel Tank Pressure sensor. Refer to Fuel Tank Pressure Sensor Replacement .

Did you complete the replacement?

--

Go to Step 18

--

17

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming .

Did you complete the replacement?

--

Go to Step 18

--

18
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 3

Go to Step 19

19

Select the Capture Info option and the Review Info option using the scan tool.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to the applicable DTC

System OK